How big will my puppy get?

Puppies grow along an S-shaped curve: slowly at first, then very fast, then levelling off as they reach adult size. In 2014 Posada, Gomez and Rosero fitted that curve to puppies of 10 breeds weighed every fortnight at a canine research centre in Colombia, using the growth model WALTHAM researchers (Hawthorne and colleagues, 2004) had used before, and published the curve's numbers for each breed.

From those numbers we worked out, for each breed, what share of its adult weight it had reached at a given week, and took the lowest and highest breed in each size band. So the estimator never gives a single figure: if a medium puppy weighs 7 kg at 24 weeks, when medium puppies are about 57 to 72% grown, its adult weight comes out at roughly 9.7 to 12.3 kg. The wider the range, the less the study can tell you.

Pick the band from the adult weight you expect: from the breed, or from the size of the parents if you know them. If you are unsure, try two bands and see how far apart the answers are.

Honestly, thin. The study behind the numbers followed 21 dogs of 10 breeds at one research centre, fed complete commercial puppy food, and some of its breed curves fitted the weights loosely. The authors themselves say a larger sample would improve the model's predictions. We use it because it publishes the curve for each breed, so every figure here can be traced.

A much larger WALTHAM study by Salt and colleagues (2017, PLoS ONE) built growth charts from the records of millions of dogs aged 12 weeks to 2 years, in five size bands up to 40 kg. Its charts are drawn as weight centiles rather than shares of adult weight, so we could not read percentages from it, and the authors say the standards still need validating before they become a clinical tool. It does confirm the pattern: very small dogs reach maturity at about 8 to 12 months, and larger breeds can take up to 24 months.

Most growth research uses pedigree dogs in Europe and the Americas. Many Indian puppies are indies or mixes whose parents' size is unknown, so their adult weight is genuinely hard to predict. PDSA notes that larger breeds can take 18 months to 2 years to reach full size, so a big-boned indie may keep filling out well past its first birthday.

A good estimate helps with practical things: the size of crate or bed to buy, the space a dog will need in a flat, and the kind of sitter or walker it will suit as an adult. Puppies should be fully vaccinated before they exercise in public places, PDSA advises, so plan walks with your vet's schedule in mind.